The present invention relates to an electric double layer capacitor and, more particularly, to a stack type electric double layer capacitor having polarizing electrodes implemented by Activated Carbon/Carbon composite (AC/C composite).
An electric double layer capacitor has a static capacity greater than one available with an aluminum electrolytic capacitor, and does not need a charge/discharge control circuit included in a secondary battery. With these advantages, this type of capacitor has customarily been used mainly to back up a memory included in an electronic apparatus and to start up a motor, actuator or similar mechanical part instantaneously at the time of power failure. Polarizing electrodes built in the capacitor are generally implemented as AC/C composite electrodes having a broad surface area, e.g., a paste of a mixture of powdery activated charcoal and electrolyte or activated charcoal fibers impregnated with an electrolyte. There has recently been proposed polarizing electrodes formed of an activated carbon/polyacene composite, as taught in Japanese Patent Laid-Open Publication No. 4-288361. This composite is produced by causing a mixture of powder or fibers of AC/C composite and granular or powdery phenol resin to set by heat, and then heating it in a nonoxidizing atmosphere. An electric double layer capacitor with this kind of polarizing electrodes can be rapidly charged and discharged by a current of the order of several amperes to several thousand amperes.
The electric double layer capacitor is often used as an instantaneous energy source for a motor, actuator or similar mechanical part needing great energy at the time of start-up. The capacitor therefore must be highly reliable, small size, and light weight. The problem with the conventional capacitor which is hermetically sealed is that when it is rapidly charged or discharged by a current as great as several amperes to several thousand amperes, Joule heat accumulates in the capacitor and deteriorates reliability. While Japanese Utility Model Laid-Open Publication No. 63-9125, for example, discloses an electric double layer capacitor for solving the above problem, it has the following problems (1)-(3) left unsolved.
(1) A heat radiation efficiency and therefore reliability achievable when the capacitor is low. PA1 (2) The capacitor is large size and heavy weight. PA1 (3) The capacitor cannot enhance productivity.
Why the problems (1)-(3) are brought about will be discussed specifically later.